High Entropy Alloys for sustainable next-generation spintronics

In a newly published study in Advanced Materials, researchers from the Max Planck Institute of Microstructure Physics report a new class of materials that may enable more sustainable spintronic devices: iridium-based high entropy alloys.

To the point:

• Crystalline Ir-based high entropy alloys (HEAs) grown at room temperature via magnetron sputtering
• Strong spin Hall effect in HEAs enables efficient current-induced magnetization switching and domain wall motion
• Environmental impact: dilution of heavy metals in HEAs offers a pathway toward sustainable spintronic devices

The study establishes high entropy alloys as a promising class of materials, with an almost limitless number of elemental combinations, for next-generation spintronic applications, offering tunable material properties, efficient spin current generation, and compatibility with existing microelectronic technologies.

Next-generation spintronic devices, such as racetrack memory, magnetic logic, and spin-based computing, will rely on materials that can efficiently convert charge currents into spin currents via the spin Hall effect. Traditionally, this role has been played by heavy metals like platinum, tantalum, or iridium, which offer strong spin Hall effects but come with limitations in tunability, cost, and environmental impact.

In the study, high-entropy alloys with significantly diluted heavy metal content are shown to be highly efficient sources of spin-orbit torques for spintronic applications. Epitaxially grown 4-, 5-, and 6-element alloy thin films are successfully integrated into magnetic racetrack memory devices, enabling efficient domain wall motion and expanding the family of materials available for spin current generation.

High entropy alloys (HEAs) are a new class of materials made by mixing multiple metallic elements (typically five or more) in nearly equal proportions. This unique composition gives rise to exceptional structural stability and tunable properties. In this study, iridium-based HEA thin films are grown in a highly crystalline state at room temperature using magnetron sputtering and are shown to be compatible with the high-quality growth of magnetic multilayers with perpendicular magnetic anisotropy.

Critically, the team demonstrated that these HEA films can generate sufficient spin-orbit torque to enable current-induced magnetization switching and domain wall motion. Using techniques like spin-torque ferromagnetic resonance and harmonic Hall measurements, the researchers quantified the efficiency of spin-charge interconversion and confirmed low switching currents (~10 MA/cm²) with high reproducibility. Additionally, domain walls in HEA-based racetracks reached speeds of up to 300 m/s under moderate current densities.

Beyond their performance, these HEAs offer a more sustainable alternative to conventional spin Hall materials by diluting the heavy metal content with other elements, representing a step toward eco-friendly spintronics without compromising functionality.